LIS 384K.11 Database-Management Principles and Applications Basic Concepts of Entity-Relationship Analysis R. E. Wyllys Last revised 2002 Feb 18 GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

What Is Entity-Relationship Analysis? E-R analysis endeavors to Identify major ingredients, entities, of a complicated situation Identify characteristics, attributes, of the major ingredients Uncover and analyze interconnections, relationships, among the major ingredients Assess various aspects of the relationships GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

E-R Analysis In short, E-R analysis strives to take a close look at the ingredients of a puzzle in order to identify major and minor ingredients and to figure out how they relate to each other GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

E-R Analysis E-R analysis can be summarized as the process of uncovering, analyzing, and explicating (i.e., stating clearly and fully) the business rules governing a complicated situation GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules Rob and Coronel1 say: Business rules are precise statements, derived from a detailed description of the organization's operations, that define one or more of the following modeling components: Entities Relationships Attributes Connectivities Cardinalities Constraints 1Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules Examples of business rules1 An invoice contains one or more invoice lines, but each invoice line is associated with a single invoice. That is, An invoice contains one or more invoice lines. Each invoice line is associated with a single invoice. A store employs many employees, but each employee is employed by only one store. A college has many departments, but each department belongs to a single college. (This business rule reflects a university that has multiple colleges such as Business, Liberal Arts, Education, Engineering, etc.) 1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules Examples of business rules1 (cont'd) A driver may be assigned to drive many different vehicles, and each vehicle can be driven by many drivers. (Note: Keep in mind that this business rule reflects the assignment of drivers over a period of time.) A client may sign many contracts, but each contract is signed by only one client. A sales representative may write many contracts, but each contract is written by one sales representative 1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules Some business rules for a library Books and other materials exist in various editions and numbers of copies Books may or may not circulate Books that circulate may do so for varying periods Periods may be determined by Book status alone Borrower status alone Combination of book status and borrower status GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules More business rules for a library Users may have various statuses Users may have varying numbers of items currently charged out to them Users may or may not owe fines Fine status may or may not affect eligibility to borrow GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules More business rules for a library Staff members have attributes of Salary or wage rates Annual leave Sick leave Work schedules Job titles Special skills (e.g., languages, puppetry) Hire dates Total length of service Professional organization memberships GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules More business rules for a library Physical facilities include Branches Furniture Machines (e.g., computers, microform readers, automobiles, players for CD-ROMs, audiotapes, videotapes) Library-management software Catalog records (e.g., computerized databases, catalog cards) Records of inventory, acquisitions, circulation, personnel GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Business Rules More business rules for a library Related organizations may include City, university, or corporate administrations Employee unions Friends of the Library organizations Vendors of books, serials, and other products and services used by the library Networks of which the library is a member (e.g., OCLC, Amigos, Association of Research Libraries, Texas State Library network, Central Texas Library System) GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

E-R Diagrams E-R analysis relies heavily on diagrams to represent Entities (rectangles) Attributes (ellipses) Relationships (diamonds) Connections (lines, which may have arrowheads or crowsfeet to represent degrees of connectivity or relationship) GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Crucial Use of E-R Analysis It is especially important to identify and note many-to-many (M:N) relationships: for example1 Note: The small circle denotes optionality (a person need not be a customer; but to be a customer, he or she must rent at least one tape) 1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Crucial Use of E-R Analysis The typical resolution of many-to-many (M:N) relationships is by a bridge table (also called a composite entity) GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

Crucial Use of E-R Analysis A further explication of the resolution of the M:N relationship GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications

E-R Analysis Is Part Science, Part Art GSLIS - The University of Texas at Austin LIS 384K.11, Database-Management Principles and Applications